1. The Field of the Invention
The present invention pertains to a method and device for assuring equal distribution of two phase flow at piping junctions and in particular to a method and device which alternately feeds the two phase flow to each of the two outlet legs of a junction.
2. The Prior Art
When a mixture of liquid and vapor enter a piping junction, such as a T junction, it often occurs that the relative proportion of vapor and liquid leaving the outlet legs of the junction is different than the proportion of the vapor and liquid entering inlet leg of the junction; the ratio of vapor and liquid at one outlet leg will be substantially higher than that at the inlet leg, while the other outlet leg will have a vapor to liquid ratio substantially lower than that at the inlet leg. This phenomenon has come to be called phase splitting in the technology of multiphase flow.
Phase splitting behavior has a detrimental effect in many industrial operations, notably the distribution of saturated or wet steam to steam injection wells in oilfield being treated with thermally enhanced oil recovery. In these operations, the ratio of the mass of vapor to the total mass is known as steam quality. It is well known in the art of thermally enhanced oil recovery that it is desirable to cause steam of equal quality to be delivered to each of the steam injection wells.
In oilfield steam distribution systems, a single steam source serves many widely distributed steam injection wells. In practice the single steam stream from the source is divided into multiple streams by ordinary piping junctions, most commonly T junctions. Unfortunately, the use of these simple junctions promotes phase splitting, which causes the liquid and vapor phases of the steam to be distributed unevenly among the injection wells; some of the wells receiving steam of a quality higher than the source steam quality and some of the wells receiving steam of a quality lower than the quality of the source.
Recently several types of apparatus have been employed in oilfield steam operations in an attempt to reduce and/or eliminate phase splitting. Several involve the use of static mixing devices, which serve to cause the liquid portion of the steam to become thoroughly mixed as tiny droplets dispersed within the vapor stream. The "pseudo-single-phase" mist stream is then divided by ordinary piping junctions or other means, some of which employ flow dividing plates or vanes. Some of these flow dividing devices incorporate a means for fixedly adjusting the position of the dividing device corresponding to the desired ratio of flow rates at the outlet legs of the junction. Other devices offer no provision for adjustment. The unfortunate and undesirable consequences of operating any of the devices which employ a mixing means is that they all cause a significant and permanent reduction in the pressure of the flow stream.
Some examples of the prior art can be found in U.S. Pat. No. 5,165,450, which shows a movable plate used to divide a single fluid stream into two streams. U.S. Pat. No. 5,251,662 shows a device having both static mixer means and a flow proportioning movable plate means. U.S. Pat. No. 5,291,911 shows another flow proportioning device utilizing conical segments.